netdev - Re: [PATCH net 1/1] net_sched: sch_fq: Fix out of range band computation

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Message-ID: <CANn89iK+4p7i_+NaLQq5S7yQ+JB=ZEUJEsxvFkzamttzm21u8A@mail.gmail.com>
Date: Wed, 13 Dec 2023 18:29:55 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jamal Hadi Salim <jhs@...atatu.com>, Willem de Bruijn <willemb@...gle.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, jiri@...nulli.us, 
	xiyou.wangcong@...il.com, netdev@...r.kernel.org, pctammela@...atatu.com, 
	victor@...atatu.com, Coverity Scan <scan-admin@...erity.com>
Subject: Re: [PATCH net 1/1] net_sched: sch_fq: Fix out of range band computation

On Wed, Dec 13, 2023 at 5:57 PM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> It is possible to compute a band of 3. Doing so will overrun array
> q->band_pkt_count[0-2] boundaries.
>
> Fixes: 29f834aa326e ("net_sched: sch_fq: add 3 bands and WRR scheduling")
> Reported-by: Coverity Scan <scan-admin@...erity.com>
> Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
> ---
>  net/sched/sch_fq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
> index 3a31c47fea9b..217c430343df 100644
> --- a/net/sched/sch_fq.c
> +++ b/net/sched/sch_fq.c
> @@ -159,7 +159,7 @@ struct fq_sched_data {
>  /* return the i-th 2-bit value ("crumb") */
>  static u8 fq_prio2band(const u8 *prio2band, unsigned int prio)
>  {
> -       return (prio2band[prio / 4] >> (2 * (prio & 0x3))) & 0x3;
> +       return (prio2band[prio / 4] >> (2 * (prio & 0x3))) % 0x3;
>  }
>

Are you sure this is needed ?

fq_load_priomap() makes sure this can not happen...